A need exists for a surgical drape, bandage or like product that kills bacteria but is itself non-toxic, that provides permanent antimicrobial capacity yet the antimicrobial agent itself is not extracted from the fabric in use and that maintains its effectiveness over a period of time but is not inhibited by sterilization, storage or handling.
A particularly useful antimicrobial agent is Q9-5700, an antimicrobial agent available from Dow Corning Corporation of Midland, Michigan. The material is a silicone quaternary amine, chemically 3-(trimethoxysilyl)-propyloctadecyl dimethyl ammonium chloride. This material has been used to protect textiles and inhibit odor-causing bacteria and fungi which contamination may result in odor problems, discoloration and deterioration of these textiles. Application of this type of silicone quaternary amine onto the surface of textiles has been found to inhibit the growth of microorganisms and to aid in the control of the above-mentioned problems. As such it is authorized by the Environmental Protection Agency of the United States Government for use on textile surfaces (EPA No. 34292-1) and it has also been accepted by the Food and Drug Administration of the U.S. Government for use in medical devices for use association with humans and animals.
Surgical drapes and like materials are typically made of non-woven textiles or other non-woven type materials, however when such silicone quaternary amines are applied to a non-woven substrate it was found that the substrate was rendered hydrophobic, thus aqueous-based fluids, including normal body fluids, were repelled by such a coated substrate. Further difficulties were encountered in maintaining the integrity of the silicone quaternary amine in or on the substrate and preventing it from leaching away from the substrate and possibly contaminating patient's surface area surrounding the site of the surgical procedure and even possibly contaminating the surgical opening itself.
The requirements for a successful medical fabric or substrate include the following:
1. The substrate must be bioactive, that is it must achieve a 95% or better bactericidal effect within one hour. In other words, the material is bacteriocidal and not merely bacteriostatic as is the case with the wearing apparel.
2. The bioactive/bactericidal material must remain on the substrate and not be leached from the substrate, but if leaching occurs it must be virtually undetectable, i.e. only less than 70 parts per billion (70 ppb) from a 6 inch.times.6 inch swatch according to test procedures, described in more detail below. Non-leachability or substantial non-leachability is a factor of the fabric sample or swatch size being tested.
3. The leachate removed from a sample of the medical substrate must not exhibit cytotoxicity to cells. This includes not only the antimicrobial agent itself but also other finishes, colorants or the like that may also be applied to the substrate. A typical testing procedure includes adding a standardized cell culture to a leachate recovered from a predetermined sample size of the substrate being tested, incubating the culture plus leachate and observing the culture for either cell death or morphological change to the cells in the culture.
4. The medical substrate must be non-flammable in accordance with standard CS-191-53.
5. The medical substrate must conform to the anti-static requirements of test NFPA 56-A.
6. The substrate itself must be absorptive of normal body fluids, such as physiological saline, and blood.
It has been a continuing difficulty in the art to identify an appropriate finishing agent or group of agents that will inhibit the hydrophobicity imparted to the substrate by the silicone quaternary amine antimicrobial agent and provide a substrate conforming to the six requirements identified above. Virtually all detergents commonly used as fabric softeners are leachable from a non-woven substrate and tend to lyse cells to at least some extent. For example, to be successfully used organic non-ionic surfactants may require a substantial amount of the surfactant on the substrate, for instance from 5 to 15%, calculated on the weight of the fabric.
Another difficulty encountered is in the selection of an appropriate substrate is that the silicone quaternary amine-type antimicrobial compounds do not readily adhere to polyester substrates and that as such the resulting product does not conform to the maximum leachability requirements, as stated above. Accordingly cellulosic substrates are preferred, although minor amounts of polyester in a cellulosic/polyester blend may be tolerated.